Magnetic field sensor

ABSTRACT

A magnetic field sensor including an amplifier and a magnetic field element for outputting a signal to a switch circuit according to the strength of an applied magnetic field. The switch circuit outputs a signal selected by an external two-phase signal to an amplifier that amplifies the signal and outputs a resulting voltage to a first end of a memory element. A switch, having one end connected to a second end of the memory element, is controlled by the two-phase signal. The switch closes in a first phase of the two-phase signal causing the memory element to store the output voltage of the amplifier, and opens in a second phase causing a vector sum of the output voltage the amplifier to be stored in the memory element and providing the output voltage to a signal output terminal connected to the second end of the memory element.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a magnetic field sensor whichcomprises a Hall element and an amplifier for amplifying the outputvoltage of the Hall element and which detects the magnetic fieldstrength in the installed location so as to output a signal inaccordance with the detected magnetic field strength.

[0002] A typical magnetic field sensor is a bipolar IC or a CMOS ICwhich include a Hall element for outputting an output voltageproportional to the magnetic field strength and an amplifier foramplifying an output voltage of the Hall element as well as a comparatorfor inputting the output voltage of the amplifier to be compared with areference potential and for outputting the comparison result. Such amagnetic field sensor outputs an output signal of two values (0 or 1)showing whether the magnetic field strength of the location where themagnetic field sensor is installed is larger or smaller than a constantreference.

[0003] Another magnetic field sensor comprises a Hall element foroutputting the output voltage proportional to the magnetic fieldstrength and an amplifier for amplifying the output voltage of the Hallelement and outputs the output signal of that amplifier as an analogsignal, without change.

[0004] One of the major factors of dispersion in characteristics amongthe products of the magnetic field sensor is the dispersion of theoffset signal component included in the output voltage of the Hallelement. This occurs due to the stress, or the like, which is receivedby the Hall element body from the package. Another one is an offsetsignal component which exists at the input terminal of the amplifier (ingeneral, a differential amplifier).

[0005] U.S. Pat. No. 4,037,150 discloses a technology which makes theinfluence of the offset signal component of the Hall element be small. Amagnetic field sensor according to the invention described in U.S. Pat.No. 4,037,150 has a Hall element in a plate form with four terminals andthe form of a Hall element is geometrically equal, as is that of theHall element 1 described in FIGS. 5 and 6.

[0006] “Geometrically equal forms” means that the form under thecondition of FIG. 5 and the form under the condition where the Hallelement of FIG. 5 is rotated by 90 degrees (it is rotated so that A-A′agrees with B-B′ in FIG. 5) are the same, as is the Hall element 1described in FIG. 5.

[0007] A description is made in reference to FIG. 5. The Hall elementhas two pairs of terminals A-A′ and B-B′ in the diagonal direction. Inthe first phase (first timing) a power source voltage is applied acrossthe terminals A-A′ and the output voltage across the terminals B-B′ isdetected so as to be stored in memory. Next, a power source voltage isapplied across the terminals B-B′ at the second phase (second timing)and the output voltage across the terminals A-A′ is detected so as to bestored in memory. The switching of these actions is implemented by theswitch circuit 24.

[0008] Here, a circuit for applying a power source voltage to the Hallelement is not shown in every figure.

[0009] The timing chart for the first and the second phases is describedin FIG. 7. A sum is gained between an output signal of the first phaseand an output signal of the second phase and, then, an effective signalcomponent of an output signal of the Hall element is added in the samephase so as to be doubled while an offset signal component of an outputsignal of the Hall element is added in the negative phase so as to bemutually canceled. In this manner, the influence given to the outputsignal by the offset signal component of the Hall element is suppressed.

[0010] Next, the configuration of a conventional magnetic field sensorwhich compensates the offset signal component due to the input offset ofthe amplifier is described in reference to FIGS. 5 and 6.

[0011]FIG. 5 shows a configuration of a magnetic field sensor accordingto the first prior art as disclosed in the Japanese unexamined patentpublication H8(1996)-201491. In FIG. 5, a Hall element is denoted as 1,a switch circuit is denoted as 24, capacitors which are memory elementsare denoted as 4 and 6, switches are denoted as 5 and 8, voltage-currentconversion amplifiers, each of which has high input and output impedanceand converts a input voltage into a current so as to be outputted, aredenoted as 10 and 11, and a resistance is denoted as 12.

[0012] In the first phase, the first phase signal (a) which has a pulseis given to the switch 5 while in the second phase, the second phasesignal (b) which has a pulse is given to the switch 8. In addition, thefirst and the second phase signals are given to the switch circuit 24.

[0013] The relationship between the first phase and the second phase inthe first prior art is shown in FIG. 7.

[0014] The operation in the first phase is described.

[0015] In the first phase the switch 5 is closed while the switch 8 isopen. At this time, a power source voltage is applied across theterminals A-A′ of the Hall element 1 so that the output voltage acrossthe terminals B-B′ is outputted through the switch circuit 24. Theoutput voltage of that Hall element 1 is inputted to the voltage-currentconversion amplifier 10.

[0016] The voltage-current conversion amplifier 10 outputs a currentwhich is proportional to the output voltage of the Hall element 1. Theoutput current IOUT of the voltage-current conversion amplifier 10 isrepresented as in the following equation.

IOUT=α(Vh+Voff10)  (1)

[0017] Voff10 is an input offset voltage of the voltage-currentconversion amplifier 10 and Vh is an output voltage of the Hall element(input voltage of the voltage-current conversion amplifier 10). α is aconversion coefficient (proportional constant) from voltage to current.

[0018] The resistance value of a Hall element has a great dispersionamong products. In general, when the resistance value of a Hall elementis small, the output voltage of the Hall element becomes large and whenthe resistance value of the Hall element is large, the output voltage ofthe Hall element becomes small.

[0019] This current flows into the capacitors 4 and 6 via the switch 5.A voltage-current conversion amplifier 11 which has the same functionsas the amplifier 10 generates a current which is proportional to adifferential voltage between the charging voltage of the capacitor 4 andthe charging voltage of the capacitor 6 and which is in the oppositedirection to the direction of a current of the voltage-currentconversion amplifier 10. Charging current to the capacitors 4 and 6stops when the sum of the respective output currents of thevoltage-current conversion amplifiers 10 and 11 becomes zero. At thistime, since the directions of the output currents of the respectivevoltage-current conversion amplifiers 10 and 11 are opposite to eachother, the absolute values of the respective output currents of thevoltage-current conversion amplifiers 10 and 11 agree. Accordingly, theoutput current IOUT2 of the voltage-current conversion amplifier 11 canbe represented in the following equation.

IOUT2=−α(Vh+Voff10)  (2)

[0020] Next, the operation in the second phase is described.

[0021] In the second phase, the switch 5 is open and the switch 8 isclosed. At this time, since the charging and discharging currents forthe capacitors 4 and 6 do not flow, the capacitors 4 and 6 maintain thecharges (accordingly, voltage) stored in the first phase. Accordingly,the voltage-current conversion amplifier 11 makes the current of thesame value as of the current in the first phase keep f lowing. Theoutput current IOUT2 of the voltage-current conversion amplifier 11 isrepresented in the equation (2).

[0022] At this time, a power source voltage is applied across theterminals B-B′ of the Hall element 1 so that the output voltage acrossthe terminals A-A′ is outputted through the switch circuit 24. Theoutput voltage of that Hall element 1 is inputted into thevoltage-current conversion amplifier 10. The output signal of that Hallelement which has been inputted into the voltage-current conversionamplifier 10 is substantially in the opposite direction to that at thetime of the first phase. Accordingly, at this time, the output currentof the voltage-current conversion amplifier 10 becomes of the sameamount and of the same polarity as of the output current of thevoltage-current conversion amplifier 11.

[0023] The output current IOUT1 of the voltage-current conversionamplifier 10 in the second phase can be represented in the followingequation.

IOUT1=α(−Vh+Voff10)  (3)

[0024] The sum current of the output currents of the voltage-currentconversion amplifiers 10 and 11 flows into the resistance 12 via theswitch 8.

[0025] Therefore, the current I which flows into the resistance 12 isgained by adding the equation (2) and the equation (3) as:

I=IOUT1+IOUT2=−2αVh  (4)

[0026] which shows that the input offset voltage Voff10 is canceled.

[0027]FIG. 6 shows the second configuration example of a conventionalmagnetic field sensor. In FIG. 6, a Hall element is denoted as 1, aswitch circuit is denoted as 24, a voltage amplifier is denoted as 25,capacitors which are memory elements are denoted as 4 and 6, andswitches are denoted as 5, 8 and 9. The capacitance values of thecapacitors 4 and 6 are equal.

[0028] The relationship among the first phase, the second phase and thethird phase according to the second prior art is shown in FIG. 8.

[0029] The operation in the first phase is described.

[0030] In the first phase, the switch 5 is closed while the switches 8and 9 are open.

[0031] At this time, power source voltage is applied across theterminals A-A′ of the Hall element 1 so that the output voltage acrossthe terminals B-B′ is outputted through the switch circuit 24. Theoutput voltage of that Hall element 1 is inputted into the voltageamplifier 25.

[0032] The voltage amplifier 25 outputs the voltage proportional to theoutput voltage of the Hall element 1. The output voltage V1 of thevoltage amplifier 25 in the first phase can be represented in thefollowing equation.

V1=β(Vh+Voff25)  (5)

[0033] Voff25 is an input offset voltage of the voltage amplifier 25 andVh is an output voltage of the Hall element (input voltage of thevoltage amplifier 25). β is a voltage amplification factor of thevoltage amplifier 25.

[0034] The capacitor 4 is charged to the output voltage V1 of thevoltage amplifier 25 via the switch 5.

[0035] Next, the operation in the second phase is described.

[0036] In the second phase, the switch 8 is closed while the switches 5and 9 are open.

[0037] A power source voltage is applied across the terminals B-B′ ofthe Hall element 1 so that the output voltage across the terminals A-A′is outputted through the switch circuit 24. The output voltage of thatHall element 1 is inputted into the voltage amplifier 25. An outputsignal of that Hall element which is inputted into the input terminal ofthe voltage amplifier 25 becomes substantially of the opposite directionto that at the time of the first phase. Accordingly, at this time, theoutput voltage V2 of the voltage amplifier 25 can be represented in thefollowing equation.

V2=β(−Vh+Voff25)  (7)

[0038] The capacitor 6 is charged to the output voltage V2 of thevoltage amplifier 25 via the switch 8.

[0039] Finally, the operation in the third phase is described.

[0040] In the third phase, the switch 9 is closed while switches 5 and 8are open.

[0041] Both terminals of the capacitor 4 are made to cross each othervia the switch 9 and are connected in parallel with both terminals ofthe capacitor 6. As a result, the average value of the voltage −V1,across the terminals of the capacitor 4, and the voltage V2, across theterminals of the capacitor 6, is outputted to the output terminal. Sincethe capacitance values of the capacitors 4 and 6 are the same, thatoutput voltage V is represented in the following equation.

V=(−V1+V2)/2=−βVh  (8)

[0042] Here, it is seen that the input offset voltage Voff25 of thevoltage amplifier 25 is canceled.

[0043] The voltage amplifier 25 of the magnetic field sensor, whichutilizes a Hall element, outputs the first output signal which is asignal gained by amplifying the output signal across the two mutuallyfacing terminals of the Hall element with four terminals in the firstphase. The voltage amplifier 25 outputs the second output signal whichis a signal gained by amplifying the output signal across the other twomutually facing terminals of the Hall element with four terminals in thesecond phase. This second output signal is substantially a signal gainedby inverting the first output signal. In this manner, the voltageamplifier of a magnetic field sensor which utilizes a Hall elementcancels the input offset voltage Voff25 of the voltage amplifier 25 byoutputting signals in the first phase and in the second phase which arein a substantially inverted relationship.

[0044] Since the output voltage of the Hall element is outputted as adifferential voltage between the two terminals of the Hall element,conventionally the differential voltage of the Hall element is inputtedinto a differential amplifier so that the differential amplifier outputsa non-inverted (plus) output signal and an inverted (minus) outputsignal.

[0045] Therefore, an amplifier of a conventional magnetic field sensoris a double output-type amplifier which has a non-inverted outputterminal and an inverted output terminal as shown in FIG. 5 or 6.

[0046] When the double output-type amplifier is used, however, theoutput part has a large number of component elements and a large chiparea is occupied.

[0047] In a conventional configuration, there is the defect that thecircuit scale for canceling the input offset voltage is large.

[0048] In addition, a magnetic field sensor has been used in productswhich are battery operated, such as cellular phones, in recent yearsand, therefore, the reduction of the consumption current of the magneticfield sensor is becoming an important technical problem. As for themeans used for the reduction of the consumption current, it is generalto adopt an intermittent operation which makes the consumption currentbe zero during a constant time by using a counter, or the like.

[0049] However, there is a constraint in the time wherein the sensoroperation can be stopped depending on the sets using the magnetic fieldsensor and, therefore, it becomes a problem of in how many steps onesensing operation can be implemented. More concretely, in the firstprior art, the magnetic field strength can be measured in the two stepsof the first and the second phases. In the second prior art the magneticfield strength can be measured in the three steps of the first to thethird phases.

[0050] The present invention is intended to solve the above describedconventional problem and has the purpose of providing a magnetic fieldsensor which reduces the dispersion of the output voltage for detectingthe magnetic field strength and which consumes a small amount of powerand is inexpensive.

SUMMARY OF THE INVENTION

[0051] The invention according to claim 1 of the present invention is amagnetic field sensor comprising:

[0052] a Hall element for outputting a signal in accordance with anapplied magnetic field strength to an output terminal;

[0053] a switch circuit for inputting the signal of said output terminalof said Hall element and for outputting a signal selected by a signalcomprising first and second phases given from the outside of said switchcircuit;

[0054] an amplifier wherein at least one input terminal is connected tothe output terminal of said switch circuit and a voltage gainedamplifying the signal of this input terminal is outputted to an outputterminal;

[0055] a first memory element of which one end is connected to saidoutput terminal of said amplifier;

[0056] a switch of which one end is connected to the other end of saidfirst memory element and which carries out opening and closingoperations by means of said signal which comprises the first and thesecond phases given from the outside of said switch; and

[0057] a signal output terminal connected to said other terminal of saidfirst memory element,

[0058] wherein said switch closes in said first phase so that said firstmemory element stores an output voltage of said amplifier and saidswitch opens in said second phase so that a vector sum of said voltagestored in said first memory element then an output voltage of saidamplifier is outputted to said output terminal.

[0059] The present invention cancels the input offset voltage of theamplifier in a simple circuit. Thereby, a compact and inexpensivemagnetic field sensor which receives no influence from that input offsetvoltage and which has little dispersion among products is attained.

[0060] In addition, the present invention attains a magnetic fieldsensor which consumes a small amount of power.

[0061] In the present specification and in the scope of the claims, theword “phase” means a timing along the time axis. The words “first phase”and “second phase” mean no more than being of mutually different timingalong the time axis.

[0062] For example, in addition to the case where the “first phase” andthe “second phase” occur repeatedly as in FIG. 7, or the like, the casewhere they occur only once when there is a request from the outside isincluded in the technical scope of the present invention.

[0063] Furthermore, in the present invention, the period of therepetition in the case that the “first phase” and the “second phase”occur repeatedly as in FIG. 7 or the like, the ratio of the length ofthe period of the first phase to that of the second phase, the length ofthe period which belongs to neither the first phase nor the secondphase, or the like, do not matter. For example, a case where a magneticfield sensor is intermittently operated at long constant intervals isalso included.

[0064] The invention according to claim 2 of the present invention is amagnetic field sensor according to claim 1, characterized in that:

[0065] said switch circuit comprises second and third memory elements;and

[0066] in said first phase of said signal given from the outside of saidswitch circuit, the output voltage of the output terminal of said Hallelement is stored in said second memory element and the voltage storedin said third memory element is given to said amplifier and, in saidsecond phase, the voltage stored in said second memory element is givento said amplifier and the voltage of the output terminal of said Hallelement is stored in said third memory element.

[0067] According to the present invention, in a simple circuitconfiguration, the differential voltage between the two terminals of theHall element is, for example, converted into a voltage relative to thepotential of one output terminal of the magnetic sensor so that thevoltage relative to the potential of this one output terminal isinputted into a single output-type amplifier. The potential of this oneoutput terminal may be a constant reference potential (including theground) or may not be a reference potential.

[0068] In the present invention, a single output-type amplifier can beutilized in place of a conventional double output-type amplifier. Thepresent invention wherein a single output-type amplifier is used has asmaller number of component elements of the output part than that of adouble output-type amplifier and, therefore, occupies only a small chiparea.

[0069] The present invention can attain a compact and inexpensivemagnetic field sensor with a low power consumption.

[0070] The single output-type amplifier amplifies the inputted signaland outputs either one of the non-inverted output signal or the invertedoutput signal.

[0071] The invention according to claim 3 of the present invention is amagnetic field sensor according to claim 1 or 2, characterized in thatat least one memory element among said memory elements is a capacitor.

[0072] According to the present invention, a magnetic field sensor usesa memory element, which is compact so as to be suitable for an IC.Thereby, a compact and inexpensive magnetic field sensor can beattained.

[0073] The invention according to claim 4 of the present invention is amagnetic field sensor according to claim 1 or 2, characterized in that:

[0074] said switch comprises first, second and third parallelconnections wherein first and second conductive characteristicstransistors are connected in parallel, and the connection between twoterminals of said first and second conductive characteristicstransistors are conducted or cut off by a binary signal given from theoutside of said switch,

[0075] wherein both ends of the second parallel connection are connectedto one end of the first parallel connection; and both ends of the thirdparallel connection are connected to the other end of the first parallelconnection; and the first conductive characteristics transistor in thefirst parallel connection is driven by a different value of the binarysignal from a value of the binary signal for driving the firstconductive transistors in the second and third parallel connections; andthe second conductive characteristics transistor in the first parallelconnection is driven by a different value of the binary signal from avalue of the binary signal for driving the second conductive transistorsin the second and third parallel connections.

[0076] According to the present invention, for example, at the time whena switch of MOS structure opens or closes in accordance with the changeof the gate terminal of the switch, the charge stored in the parasiticcapacitor across the gate and the source or across the gate and thedrain of the switch can be prevented from flowing out into or flowing infrom the memory element.

[0077] Thereby, a magnetic field sensor with little dispersion can beattained.

[0078] The invention according to claim 5 of the present invention is amagnetic field sensor according to claim 1 or 2, characterized in thatat least one of the resistances for defining the gain of the amplifieris an element of which the manufacturing process is identical to that ofthe Hall element.

[0079] In a magnetic field sensor according to the present invention, atleast one resistance among the resistances for defining the gain of thevoltage amplifier is formed of an element of which the manufacturingprocess is identical to that of the Hall element, and the Hall elementand the voltage amplifier are included in the same semiconductor chip.

[0080] When the resistance value of a Hall element is small, theresistance value of the resistance made of this identical elementbecomes small and the magnetic field sensor is configured so that thegain of the voltage amplifier becomes small as a result. On thecontrary, when the resistance value of the Hall element is large, theresistance value of the resistance made of this identical elementbecomes large and the gain of the voltage amplifier becomes large as aresult.

[0081] Thereby, the effect is obtained that a magnetic field sensor canbe attained wherein the dispersion of the output voltage is smaller thanthe dispersion of the resistance value of the Hall element.

[0082] In the description of the present specification and the scope ofthe claims, “element of which the manufacturing process is identical”means an element produced through the same manufacturing process. Forexample, it means to go through the diffusion step of the identicalimpurities or to produce the identical N well. The differences inphysical dimensions or forms of the elements do not matter. Accordingly,in the case that a Hall element and a resistance are the elementsmanufactured through the identical manufacturing process, they are theelements of which the manufacturing processes are identical even if thedimensions or the forms of the Hall element and the resistance aredifferent.

[0083] The invention according to claim 6 of the present invention is amagnetic field sensor characterized by comprising:

[0084] a Hall element which outputs a signal in accordance with anapplied magnetic field strength;

[0085] an amplifier which amplifies the output signal of this Hallelement and outputs a voltage signal across a pair of output terminals;

[0086] a condenser of which both ends are connected to the pair of theoutput terminals of said amplifier;

[0087] a switch part which is inserted and makes a connection betweenone of said output terminals in the pair and one terminal of saidcondenser and which is closed by a first signal given from the outsideof said switch part and is opened by a second signal given from theoutside of said switch part; and

[0088] an output terminal which outputs the voltages of both ends ofsaid switch, respectively,

[0089] wherein the polarities of the voltage signals for the pair of theoutput terminals of said amplifier during the period of said firstsignal and during the period of said second signal are mutually oppositepolarities.

[0090] The present invention cancels the input offset voltage of theamplifier with a simple circuit. Thereby, a compact and inexpensivemagnetic field sensor is attained which receives no influence of thisinput offset voltage and which has little dispersion among products.

[0091] The invention according to claim 7 of the present invention is amagnetic field sensor characterized by comprising:

[0092] a Hall element which outputs signals to first and second terminalpairs in accordance with an applied magnetic field strength;

[0093] first and second condensers;

[0094] a first connection part which connects terminals of said firstterminal pair and both ends of said first condenser, respectively;

[0095] a second connection part which connects terminals of said secondterminal pair and both ends of said second condenser, respectively;

[0096] a first switch part which is inserted and makes a connection insaid first connection part and which closes this first connection partby means of a first signal given from the outside of said first switchpart and opens this first connection part by means of a second signalgiven from the outside of said first switch part;

[0097] a second switch part which is inserted and makes a connection insaid second connection part and which opens this second connection partby means of said first signal given from the outside of said secondswitch part and closes this second connection part by means of saidsecond signal given from the outside of said second switch part;

[0098] an amplifier which amplifies a signal given to an input terminalso as to output to an output terminal;

[0099] a first output terminal;

[0100] a third connection part which connects both ends of said firstcondenser to the input terminal of said amplifier as well as to saidfirst output terminal, respectively;

[0101] a fourth connection part which connects both ends of said secondcondenser to the input terminal of said amplifier as well as to saidfirst output terminal, respectively;

[0102] a third switch part which is inserted and makes a connection insaid third connection part and which opens this third connection part bymeans of said first signal given from the outside of said third switchpart and closes this third connection part by means of said secondsignal given from the outside of said third switch part;

[0103] a fourth switch part which is inserted and makes a connection insaid fourth connection part and which closes this fourth connection partby means of said first signal given from the outside of said fourthswitch part and opens this fourth connection part by means of saidsecond signal given from the outside of said fourth switch part;

[0104] a second output terminal;

[0105] a third condenser of which one end is connected to the outputterminal of said amplifier and of which the other end is connected tosaid second output terminal; and

[0106] a fifth switch part of which both ends are connected respectivelyto said first and second output terminals and which is closed by saidfirst signal given from the outside of said fifth switch part and isopened by said second signal given from the outside of said fifth switchpart;

[0107] wherein a signal is extracted across said first and second outputterminals.

[0108] The present invention converts a differential voltage between twoterminals of the Hall element into a voltage from the potential of oneoutput terminal of the magnetic field sensor with a simple circuitconfiguration, and inputs this voltage from the potential of one outputterminal of the magnetic field sensor into a single output-typeamplifier. As for the amplifier which amplifies the voltage from thepotential of one output terminal of the magnetic field sensor, a singleoutput-type amplifier can be utilized.

[0109] The potential of one output terminal of the magnetic field sensormay be a constant reference potential or may not be a constant referencepotential.

[0110] The present invention cancels the input offset voltage of theamplifier with a simple circuit. Thereby, a compact and inexpensivemagnetic field sensor is attained which receives no influence of thisinput offset voltage and which has little dispersion among products.

[0111] The invention according to claim 8 of the present invention is amagnetic field sensor according to claim 7, characterized by comprising:

[0112] a comparator that converts the results of the comparison of thedifferential signal of said input signals which enter from said firstoutput terminal and said second output terminal respectively with apredetermined voltage into binary signals so as to output; and

[0113] a latch circuit which inputs the output signal of said comparatorand said second signal, and outputs either value of said binary signal,synchronized with one phase of said second signal.

[0114] The invention according to claim 8 can, additionally, latch theinput voltage at the timing when the second phase ends and can output aconstant digital value of 0 or 1.

[0115] The invention according to claim 9 of the present invention is amagnetic field sensor characterized by comprising:

[0116] a Hall element which outputs a signal in accordance with anapplied magnetic field strength;

[0117] an amplifier which amplifies the output signal of this Hallelement and outputs a voltage signal to an output terminal pair;

[0118] a condenser of which respective terminals are connected to theterminals of the output terminal pair of said amplifier;

[0119] a switch which is inserted to make a connection with one terminalof said output terminal pair and one terminal of said condenser andwhich is closed by a first signal given from the outside of said switchand is opened by a second signal given from the outside of said switch;

[0120] output terminals which output voltages of both ends of saidswitch respectively;

[0121] a comparator which inputs signals of these output terminalsrespectively and converts the results of the comparison of thedifferential signal of said input signals with a predetermined voltageinto a binary signal so as to output; and

[0122] a latch circuit which inputs said binary signal and said secondsignal, and outputs either value of said binary signal, synchronizedwith one phase of said second signal,

[0123] wherein the polarities of the voltage signals of the outputterminal pair of said amplifier between the period of said first signaland the period of said second signal are of mutually oppositepolarities.

[0124] The invention according to claim 9 can cancel the input offsetvoltage of the amplifier with a simple circuit and can latch the inputvoltage at the timing when the second phase ends so as to output aconstant digital value of 0 or 1.

[0125] The invention according to claim 10 of the present invention is amagnetic field sensor according to claim 8 or 9, characterized in thatpredetermined voltage of said comparator varies depending on the outputsignal of said latch circuit.

[0126] The invention according to claim 10 can extract from acomparator, a signal which is stable against noise signals and of whichthe chattering is suppressed by providing the reference value set forthe judgment by the comparator with a hysteresis. By giving this signalto a latch circuit, a stable signal which has a high judgment precisioncan be extracted from the latch circuit.

[0127] Though the novel characteristics of the invention are nothingmore than the particular description in the attached claims, the presentinvention with respect to both the configuration and the contents,together with other purposes or characteristics, will be betterunderstood and evaluated by means of the following detailed descriptionwhich is to be understood in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0128]FIG. 1 is a configuration diagram of a magnetic field sensoraccording to the first embodiment of the present invention;

[0129]FIG. 2 is a configuration diagram of a magnetic field sensoraccording to the second embodiment of the present invention;

[0130]FIG. 3 is a configuration diagram of a magnetic field sensoraccording to the third embodiment of the present invention;

[0131]FIG. 4 is a configuration diagram of a switch according to thepresent invention;

[0132]FIG. 5 is a configuration diagram of a magnetic field sensoraccording to the first prior art;

[0133]FIG. 6 is a configuration diagram of a magnetic field sensoraccording to the second prior art;

[0134]FIG. 7 is a timing chart according to the first prior art as wellas the first, the second and the third embodiments; and

[0135]FIG. 8 is a timing chart according to the second prior art.

[0136] It must be taken into account that part of, or the entirety of,the drawings are depicted in schematic representation for the purpose ofillustration and do not, necessarily, faithfully depict the relativesizes or the positions of the elements therein.

DETAILED DESCRIPTION OF THE INVENTION

[0137] In the following, embodiments of the present invention aredescribed in reference to the drawings.

[0138] <<Embodiment 1>>

[0139]FIG. 1 shows a configuration of a magnetic field sensor accordingto the first embodiment of the present invention. In FIG. 1, a Hallelement is denoted as 1, a switch circuit is denoted as 2, a voltageamplifier is denoted as 3, a capacitor which is a memory element isdenoted as 4 and a switch is denoted as 5.

[0140] The Hall element 1 is a Hall element in a plate form with fourterminals, and the form of the Hall element 1 is geometricallyequivalent.

[0141] The first phase signal (a) that has a pulse in the first phase isgiven to the switch 5 and the switch circuit 2. The second phase signal(b) that has a pulse in the second phase is given to the switch circuit2.

[0142] The timing chart in the first embodiment is shown in FIG. 7.

[0143] With respect to the magnetic field sensor constructed as theabove, the operation is described in the following.

[0144] The operation of the first phase is described.

[0145] In the first phase, the switch 5 is closed.

[0146] At this time, a power source voltage is applied across theterminals A-A′ of the Hall element 1, and the output voltage across theterminals B-B′ is outputted through the switch circuit 2. The outputvoltage of this Hall element 1 is inputted into the voltage amplifier 3.

[0147] The voltage amplifier 3 outputs the voltage which is proportionalto the output voltage Vh of the Hall element 1. The output voltage V1 ofthe voltage amplifier 3 in the first phase can be represented in thefollowing equation:

V1=β(Vh+Voff3)  (9)

[0148] Voff3 is an input offset voltage of the voltage amplifier 3 whileβ is a voltage amplification factor of the voltage amplifier 3. Bothends of the capacitor 4 are charged to the output voltage V1 of thevoltage amplifier 3 via the switch 5.

[0149] Next, the operation in the second phase is described.

[0150] In the second phase, the switch 5 is open.

[0151] The power source voltage is applied across the terminals B-B′ ofthe Hall element 1 and the output voltage across the terminals A-A′ isoutputted via the switch circuit 2. The output voltage of this Hallelement 1 is inputted to the voltage amplifier 3. The output signal ofthis Hall element which is inputted into the input terminal of thevoltage amplifier 3 becomes, substantially, of the opposite direction tothat in the first phase. Accordingly, at this time, the output voltageV2 of the voltage amplifier 3 can be represented in the followingequation:

V2=β(−Vh+Voff3)  (10)

[0152] In the second phase, the voltage across the terminals of thecapacitor 4 is maintained and is added in vector to the output voltageof the voltage amplifier 3. The signal V, as a result of vectoraddition, is outputted from the output terminals 20, 21.

[0153] Accordingly, the output voltage V of the first embodiment in FIG.1 can be represented in the following equation:

V=−V1+V2=−2βVh  (11)

[0154] It can be seen that, in the output voltage V, the input offsetvoltage Voff3 is canceled.

[0155] Judging from the comparison of the equations (4), (8) and (11),though all of the input offset voltages Voff are canceled in the samemanner, the magnetic field sensor according to the present invention hasa more compact and simpler circuit configuration in comparison with theprior art of FIG. 5.

[0156] In addition, the present invention outputs an amplified signal ofthe detected signal by the Hall element in two steps (first phase andsecond phase), which is fewer than the number of steps (three) of thesecond prior art as shown in FIGS. 6 and 8.

[0157] For example, in a device, wherein a magnetic field sensor of thepresent invention is applied, which outputs an amplified signal of thedetection signal by the Hall element once for every constant period,power consumption can be reduced during a constant period in comparisonwith the device which uses a magnetic field sensor in FIG. 6 by haltingthe power source supply to the magnetic field sensor during the periodwhen the magnetic field sensor is not in operation.

[0158] <<Embodiment 2>>

[0159]FIG. 2 shows a configuration of a magnetic field sensor accordingto the second embodiment of the present invention. In FIG. 2 a Hallelement is denoted as 1, a switch circuit is denoted as 2, a voltageamplifier is denoted as 3, capacitors which are memory elements aredenoted as 4, 6 and 7, and switches are denoted as 5 and 8.

[0160] The Hall element 1 is a Hall element in a plate form with fourterminals, and the form of the Hall element 1 is geometricallyequivalent.

[0161] The voltage amplifier 3 is formed of a single input amplifier andtwo resistances 22, 23 which define the amplification factor (feed backamount). This is the same as the voltage amplifier 3 of the firstembodiment with respect to the function which outputs a voltageproportional to the input voltage.

[0162] In the first phase, the first phase signal (a) which has a pulseis given to the switch 5 (including the switch 5 which forms a part ofthe switch circuit 2) and a changing switch of a circuit which appliesthe power source voltage to the Hall element 1 (included in the switchcircuit 2 and not shown). In the second phase, the second phase signal(b) which has a pulse is given to the switch 8 (forming a part of theswitch circuit 2) and a changing switch of a circuit which applies thepower source voltage to the Hall element 1 (included in the switchcircuit 2 and not shown).

[0163] The timing chart in the second embodiment is the same as thetiming chart of FIG. 7.

[0164] As for the magnetic field sensor formed as above, the operationis described in the following.

[0165] The operation in the first phase is described.

[0166] In the first phase, the switch 5 is closed while the switch 8 isopen.

[0167] At this time, the power source voltage is applied across theterminals A-A′ of the Hall element 1 and the output voltage Vh acrossthe terminals B-B′ is outputted to the switch circuit 2. The outputvoltage Vh of this Hall element 1 is applied to the capacitor 6 throughthe switch 5 so as to charge the capacitor 6.

[0168] At this time, the voltage across both ends of the capacitor 7 isinputted into the input terminal of the voltage amplifier 3 through theswitch 5.

[0169] One input terminal of a single output-type voltage amplifier 31which forms the amplifier 3 is connected to one output terminal of themagnetic field sensor.

[0170] The single output-type voltage amplifier 31 outputs a voltageproportional to the voltage across both ends of the capacitor 7. Asdescribed below, the voltage across both ends of the capacitor 7 is Vh.The output voltage V1 of the voltage amplifier 3 in the first phase canbe represented in the following equation. This is the same as the aboveequation (9).

V1=β(Vh+Voff3)  (12)

[0171] Here, β, Vh and Voff3 are defined in the same manner as in thefirst embodiment.

[0172] Both ends of the capacitor 4 are charged to the output voltage V1of the voltage amplifier 3 via the switch 5.

[0173] Next, the operation in the second phase is described.

[0174] In the second phase, the switch 8 is closed while the switch 5 isopen.

[0175] At this time, the power source voltage is applied across theterminals B-B′ of the Hall element 1 and the output voltage Vh acrossthe terminals A-A′ is outputted to the switch circuit 2. The outputvoltage Vh of this Hall element 1 is applied to the capacitor 7 throughthe switch 8 so as to charge the capacitor 7.

[0176] At this time, the voltage across both ends of the capacitor 6 isinputted to the input terminal pair (input terminal of the singleoutput-type voltage amplifier 31 and minus output terminal 21 of themagnetic field sensor) of the voltage amplifier 3 through the switch 8.

[0177] The single output-type voltage amplifier 31 outputs a voltageproportional to the voltage across both ends of the capacitor 6. Thevoltage across both ends of the capacitor 6 is Vh. The output voltage V2of the voltage amplifier 3 in the second phase can be represented in thefollowing equation. This is the same as the above equation (10).

V2=β(−Vh+Voff3)  (13)

[0178] In the second phase, the voltage across the terminals of thecapacitor 4 is maintained and is added in vector to the output voltageof the voltage amplifier 3. The signal V as a result of the vectoraddition is outputted from the output terminals 20, 21.

[0179] Accordingly, the output voltage V of the second embodiment inFIG. 2 can be represented in the following equation.

V=−V1+V2=−2βVh  (14)

[0180] It can be seen that, in the output voltage V, the input offsetvoltage Voff3 is canceled.

[0181] The magnetic field sensor of the second embodiment repeatedlycarries out the above operation.

[0182] In this manner, according to the present invention, the outputvoltage Vh across the output terminals B-B′ is once stored in thecapacitor 6 in the first phase. In the second phase, the connectionbetween the capacitor 6 and the Hall element is cut and one terminal ofthe capacitor 6 is connected to the minus output terminal 21 of themagnetic field sensor while the other terminal of the capacitor 6 isconnected to the non-inverted (plus) input terminal of the singleoutput-type amplifier 31.

[0183] In the same manner, the output voltage across the outputterminals A-A′ is stored in the capacitor 7 in the second phase. In thefirst phase, the connection between the capacitor 7 and the Hall elementis cut and one terminal of the capacitor 7 is connected to the minusoutput terminal 21 of the magnetic sensor while, at the same time, theother terminal is connected to the non-inverted input terminal of thesingle output-type amplifier 31.

[0184] Since the capacitor 6 maintains the voltage across both terminalsbefore and after the connection switching of both terminals, the outputvoltage Vh across the terminals A-A′ and B-B′ of the Hall element 1 isconverted to the voltage Vh with the potential of the minus outputterminal 21 as a reference (conversion of the offset level).

[0185] Thereby, a single output-type amplifier of a single input can beutilized as the voltage amplifier 3 in place of a double output-typeamplifier of a differential input.

[0186] The potential of said minus output terminal may be the referencepotential or may not be a reference potential. A plus output terminalmay be used in place of the minus output terminal (in this case, theoutput signal of the single output amplifier is outputted from the minusoutput terminal).

[0187] In the second embodiment, after disconnecting the capacitor 6 or7 from the Hall element 1, the voltage across both ends of the capacitor6 or 7 is inputted to the single output-type amplifier 31. Thereby, thedifferential voltage between the two terminals of the Hall element canbe maintained and the disconnected Hall element 1 can operate normally.

[0188] In this manner, a single output-type amplifier can be utilized inplace of a conventional double output-type amplifier.

[0189] In addition, in a magnetic field sensor of which the potential ofthe minus output terminal is not a constant reference potential(including the ground) a single output-type amplifier can be utilizedaccording to the present invention.

[0190] Preferably, feedthrough measures are taken for the switches ofEmbodiment 1 or Embodiment 2. The switches, for which the feedthroughmeasures are taken, prevent the charge stored in the parasiticcapacitance across the gate and the source, or across the gate and thedrain of the switches, from flowing out into or flowing in from thecapacitor 6 or 7 when the gate terminals of these switches are changed.

[0191]FIG. 4 is a diagram wherein feedthrough measures are taken for abi-directional switch 50 of the MOS structure, of which the gate isdriven by a binary voltage.

[0192] In the switches 50, 51 and 52, N channel and P channel MOStransistors are connected in parallel, while the gate of each transistoris driven by a binary voltage given from the outside of these switches.Here, the input and output parts of the switches 51 and 52 are connectedin common. In addition, the switch 51 is connected to one of theinput/output part of the switch 50 while the switch 52 is connected tothe other input/output part of the switch 50. When the voltage of thegate terminal of the switch 50 changes, the charge moves which is storedin the parasitic capacitance across the source, the drain and the gateof each of the N channel and P channel MOS transistors of the switch 50.Therefore, the switches 51, 52 are driven by a binary voltage of thepolarity that is opposite to that of the binary voltage which drives theswitch 50. Thereby, the charge of the parasitic capacitance in theswitches 51, 52 is moved in the direction opposite to that of the switch50. Through this movement of the charge, the movement of the charge inthe switch 50 can be canceled.

[0193] Preferably, at least one of the resistances which define thegains of the voltage amplifiers of Embodiment 1 or Embodiment 2 isformed of the same material as that of the Hall element. For example,citing the voltage amplifier 3 of FIG. 2 as an example, the resistance22 inserted between the output terminal of the single output-typeamplifier 31 and the inverted (minus) input terminal of amplifier isformed of the same element as the Hall element 1.

[0194] For example, N-type impurities are diffused into a P-typesemiconductor substrate so as to form a Hall element and a resistance 22and a resistance 23 is formed of a polysilicon resistance which haslittle dispersion.

[0195] In a magnetic field sensor which includes a Hall element 1 and avoltage amplifier 3 on the same semiconductor chip, when the resistancevalue of the Hall element 1 is small, the output voltage of the Hallelement 1 becomes large, the resistance value of this resistance 22,which is made of the same element, also becomes small and, as a result,the gain of the voltage amplifier 3 becomes small. On the contrary, whenthe resistance value of the Hall element 1 is large, the output voltageof the Hall element 1 becomes small, the resistance value of thisresistance 22, which is made of the same element, also becomes largeand, as a result, the gain of the voltage amplifier 3 becomes large.

[0196] Thereby, the gain of the voltage amplifier 3 suppresses thedispersion of the output voltage of the terminals 20, 21 in accordancewith the dispersion of the output voltage of the Hall element 1 due tothe dispersion of the resistance value of the Hall element 1. A magneticfield sensor of which the output voltage dispersion of the terminals 20,21 is small, can be attained.

[0197] <<Embodiment 3>>

[0198]FIG. 3 illustrates a magnetic field sensor of the third embodimentwhich uses the magnetic field sensor of the first embodiment accordingto the present invention. The magnetic field sensor of the thirdembodiment outputs a binary digital signal of 0 or 1 in accordance withthe intensity of the magnetic field.

[0199] In FIG. 3, a Hall element is denoted as 1, a switch circuit isdenoted as 2, a voltage amplifier is denoted as 3, a capacitor which isa memory element is denoted as 4, a switch (which is closed in the firstphase and is open in the other phase) is denoted as 5, a comparator isdenoted as 13, a latch circuit is denoted as 14, a clock generationcircuit is denoted as 15, the first phase clock generation circuit isdenoted as 16 and the second phase clock generation circuit is denotedas 17.

[0200] The Hall element 1 has a plate form with four terminals, and theform of the Hall element 1 is geometrically equivalent.

[0201] (a) in FIG. 7 shows a waveform (including the first phase) of theoutput signal obtained from the first phase clock generation circuit 16while (b) in FIG. 7 shows a waveform (including the second phase) of theoutput signal obtained from the second phase clock generation circuit17.

[0202] With respect to the magnetic field sensor formed as describedabove, the operation is described in the following.

[0203] In this description, the case is assumed that a constant magneticfield passes through the Hall element 1 and the output voltage of theHall element is constant when the offset is not taken intoconsideration.

[0204] First, a clock which determines the first phase is generated inthe first phase clock generation circuit 16. Next, by using this clock,a voltage is applied across the terminals which make a pair on adiagonal line of the Hall element 1, so that an output voltage of theHall element which is proportional to the magnetic field strength isgenerated across the other two terminals. The switch circuit 2 isoperated so that this output voltage is applied to the two inputterminals of the voltage amplifier 3. At this time, a voltage which isproportional to the output voltage of the Hall element 1 is generated inthe output of the voltage amplifier 3, which is taken into the capacitor4 via the switch 5 controlled by the first phase clock generationcircuit 16. After the end of the first phase, the switch circuit 5 isopened and the output voltage of the voltage amplifier 3 in the firstphase is maintained in the capacitor 4.

[0205] Next, a clock which determines the second phase is generated inthe second phase clock generation circuit 17. Next, by using this clock,a voltage is applied across the terminals of the Hall element 1 whereinthe output voltage across these terminals of the Hall element ismeasured in the first phase, and the other two terminals are connectedto the voltage amplifier 3. In addition, the switch circuit 2 isoperated so that the output voltage of the Hall element, which hasopposite polarity (positive or negative) to that in the first phase, isgiven to the input of the voltage amplifier 3. At this time, the outputvoltage from the voltage amplifier 3 is the reverse voltage of that inthe first phase. In addition, since the switch 5 is open, the vector sumof the output voltage of the voltage amplifier 3 in the first phasewhich is stored in the capacitor 4 and the output voltage of the voltageamplifier 3 in the second phase is connected across the input terminalsof the comparator 13.

[0206] Then, the differential voltage applied to the input terminals ofthe phase comparator 13 in this second phase becomes, as describedabove, −2βVh with the input offset voltage Voff3 being canceled.

[0207] This value is compared with the reference value set in thecomparator 13 and the judgment result (A digital signal is 0 in the casethat this value is smaller than the reference value and a digital signalis 1 in the case that this value is larger than the reference value.) isoutputted to the output terminal of the comparator 13.

[0208] The latch circuit 14 is connected to the second phase clockgeneration circuit 17 and is set so as to latch the input voltage at theend timing of the second phase. Accordingly, a constant value (digitalvalue of 0 or 1), which is maintained until the end time of the nextsecond phase, is outputted to the output terminal 18.

[0209] In addition, it is preferable to return the output value of thisoutput terminal 18 to the comparator 13 so as to set a hysteresis in thejudgment reference value for chattering prevention.

[0210] The present invention cancels the input offset voltage of theamplifier with a simple circuit. Thereby, the advantageous effects canbe obtained attaining a compact and inexpensive magnetic field sensorwhich receives no influence of that input offset voltage and has littledispersion.

[0211] In addition, according to the present invention, an advantageouseffect can be obtained attaining a magnetic field sensor of low powerconsumption.

[0212] The present invention converts the output signal of thedifferential voltage of the Hall element into a voltage relative to thereference potential, or the like, with a simple circuit and inputs thisvoltage, relative to the reference potential, or the like, into a singleoutput-type amplifier.

[0213] Thereby, a magnetic field sensor is attained wherein the outputsignal of the differential voltage of the magnetic field sensor isamplified by a single output-type amplifier of which the circuit of theoutput part is simple and occupies a small chip area.

[0214] According to the present invention, an advantageous effect can beobtained attaining a compact and inexpensive magnetic field sensor.

[0215] According to the present invention, a magnetic field sensor canbe attained wherein a compact memory element is used, which is suitablefor an IC. Thereby, an advantageous effect can be obtained attaining acompact and inexpensive magnetic field sensor.

[0216] According to the present invention, an advantageous effect can beobtained attaining a magnetic field sensor of which the dispersion ofthe output voltage due to the dispersion of the capacitance of thecapacitor is small.

[0217] According to the present invention, an advantageous effect can beobtained attaining a magnetic field sensor wherein the dispersion of theoutput voltage is smaller than the dispersion of the resistance value ofthe Hall element.

[0218] Though the invention is described with respect to preferablemodes, to a certain degree of detail, the present disclosure contents ofthose preferable modes should be changed in the details of theconfiguration and the modification of the combination or the order ofrespective elements can be attained without deviating from the claimedscope and the spirit of the invention.

What is claimed is:
 1. A magnetic field sensor characterized bycomprising: a magnetic field element which outputs a signal inaccordance with an applied magnetic field strength in first and secondphases of a signal given from the outside of said magnetic fieldelement, wherein polarities of the signal from said magnetic fieldelement in said first phase and said second phase are mutually opposite;an amplifier which amplifies the signal from this magnetic field elementand outputs a voltage signal across a pair of output terminals; acondenser of which both ends are connected to the pair of outputterminals of said amplifier; a switch which is inserted and makes aconnection between one of said output terminals in the pair and oneterminal of said condenser, and which is closed in said first phase ofthe signal and is opened in said second phase of the signal; and acomparator which inputs voltage across both ends of said switch andconverts a result of the comparison of the voltage across both ends ofsaid switch with a predetermined voltage into a binary signal so as tooutput.
 2. A magnetic field sensor according to claim 1, characterizedby further comprising: a latch circuit which inputs said binary signaland outputs an either value of said binary signal, which is latched atthe timing synchronized with a phase within said second phase of thesignal.
 3. A magnetic field sensor according to claim 1, characterizedin that said predetermined voltage of said comparator varies dependingon the output signal of said latch circuit.
 4. A magnetic field sensoraccording to claim 1, characterized in that said magnetic field elementis a Hall element.
 5. A magnetic field sensor according to claim 1characterized by further comprising a switch circuit for inputting asignal from said magnetic field element and outputting the signal tosaid amplifier, wherein said switch circuit comprises first and secondand memory elements; and in said first phase of the signal, the outputvoltage from said magnetic field element is stored in said first memoryelement and the voltage stored in said second memory element is given tosaid amplifier and, in said second phase of the signal, the voltagestored in said first memory element is given to said amplifier and thevoltage from said magnetic field element is stored in said second memoryelement.
 6. A magnetic field sensor according to claim 5, characterizedin that at least one memory element among said memory elements is acapacitor.
 7. A magnetic field sensor according to claim 1 characterizedin that: said magnetic field element outputs the signal from a firstterminal pair in said first phase of the signal and the signal from asecond terminal pair in said second phase of the signal in accordancewith the applied magnetic field strength; and a magnetic field sensorfurther comprises a switch circuit for inputting the signal from saidmagnetic field element and outputting the signal to said amplifier,wherein said switch circuit comprises: first and second condensers; afirst connection part which connects terminals of said first terminalpair and both ends of said first condenser, respectively; a secondconnection part which connects terminals of said second terminal pairand both ends of said second condenser, respectively; a first switchpart which is inserted and makes a connection in said first connectionpart and which closes this first connection part in said first phase andopens this first connection part in said second phase; a second switchpart which is inserted and makes a connection in said second connectionpart and which opens this second connection part in said first phase andcloses this second connection part in said second phase; a thirdconnection part which connects both ends of said first condenser to theinput terminal of said amplifier as well as to one output terminal ofsaid amplifier, respectively; a fourth connection part which connectsboth ends of said second condenser to the input terminal of saidamplifier as well as to said output terminal of said amplifier,respectively; a third switch part which is inserted and makes aconnection in said third connection part and which opens this thirdconnection part in said first phase and closes this third connectionpart in said second phase; and a fourth switch part which is insertedand makes a connection in said fourth connection part and which closesthis fourth connection part in said first phase and opens this fourthconnection part in said second phase.
 8. A method for detecting magneticfield comprising the steps of: (a) outputting a signal according to anapplied magnetic field strength through a magnetic field element in afirst signal period; (b) outputting the signal according to the appliedmagnetic field strength through said magnetic field element in a secondsignal period, wherein polarities of the signals according to theapplied magnetic field strength in said first signal period and saidsecond signal period are mutually opposite; (c) amplifying the signalfrom said magnetic field element in said first signal period foroutputting a voltage signal across a pair of output terminals of anamplifier and inputting a signal of the pair of output terminals of saidamplifier to both ends of a condenser; (d) amplifying the signal fromsaid magnetic field element in said second signal period for outputtinga voltage signal across a pair of output terminals of said amplifier andinputting a signal of one output terminal in the pair to one end of saidcondenser, and outputting a signal across the other end of saidcondenser and the other output terminal of said amplifier; (e) comparingthe signal across the other end of said condenser and the other outputterminal of said amplifier with a predetermined voltage; and (f)converting the results of the comparison of the signal into a binarysignal so as to output.
 9. A method for detecting magnetic fieldaccording to claim 8, characterized by further comprising a step of: (g)latching said binary signal at the timing synchronized with a phasewithin said second signal period and outputting an either value of saidbinary signal.
 10. A method for detecting magnetic field according toclaim 8, characterized by further comprising a step of: (h) varying saidpredetermined voltage in accordance with the output signal of saidlatching step.
 11. A method for detecting magnetic field according toclaim 8, characterized in that said magnetic field element outputs asignal in accordance with a Hall effect.
 12. A method for detectingmagnetic field according to claim 8, characterized by further comprisinga step of: (i) halting a power source supply to the magnetic fieldelement in every constant period.